In general, aircraft possess a nosewheel undercarriage that includes a steerable bottom portion carrying the wheels of the undercarriage and associated with a steering control for steering the steerable bottom portion on the ground in order to facilitate movements of the aircraft. The invention relates more particularly to direct undercarriages in which the bottom portion forms the sliding portion of the shock absorber of the undercarriage.
When the undercarriage is extended prior to landing, the bottom portion is kept pointing straight ahead, i.e. on the axis of the aircraft, by means of cams arranged on the bottom portion and on the non-steerable portion of the undercarriage, the cams being held in co-operation by the pressure inside the shock absorber.
When the aircraft lands, the bottom portion of the undercarriage is pushed into the undercarriage so that the cams move apart. Once the speed of the aircraft has dropped below a given threshold, steering control is activated, while continuing to keep the bottom portion of the undercarriage pointing straight ahead until the pilot starts steering the wheels.
Nevertheless, there is a risk of one of the tires being deflated or bursting during the stage in which steering is not being controlled. Under such conditions, the bottom portion swivels under the effect of the drag due to greater ground friction applied to the wheel having the properly inflated tire, and this can lead to the wheels being put at right angles relative to the direction of travel, thereby bursting the tires and damaging the rims of the wheels.
In addition, while taxiing after landing or before takeoff, significant deflation or bursting of one of the tires runs the risk of deflecting the aircraft or of damaging the undercarriage because of a sudden swiveling lurch.